This invention relates to a combined starting and shutoff device for steam and gas turbines and more particularly concerns a rapid opening valve for steam turbines. The control valve itself is fluid-pressure operated and controlled by means of an auxiliary valve. In the starting and rapid shutoff systems which serve steam turbines, there are used rapid opening valves in those steam paths where, for operational reasons, the steam flow must not be interrupted even for a short period.
The function of the rapid opening valve is that upon intentional or unintentional actuation of the rapid shutoff valve of the turbine, the steam path is, possibly without delay, directed through a bypass around the turbine to its low pressure side. For this reason, the setting periods of the rapid opening valve must be adapted to those of the rapid shutoff valve.
By the nature, rapid opening valves are, as a rule, in use only during operational malfunctionings or during the starting and stopping phases of the steam turbine so that most of the time they are in a closed state. Conventional rapid opening valves with hydromechanical drive are therefore exposed, due to their spindle arrangements, packing devices, etc., to conditions which may adversely affect the operational safety.